<?php

include_once "errorCode.php";

/**
 * PKCS7Encoder class
 *
 * 提供基于PKCS7算法的加解密接口.
 */
class PKCS7Encoder
{
    public static $block_size = 32;

    /**
     * 对需要加密的明文进行填充补位
     * @param $text 需要进行填充补位操作的明文
     * @return 补齐明文字符串
     */
    public function encode($text)
    {
        $block_size = PKCS7Encoder::$block_size;
        $text_length = strlen($text);
        //计算需要填充的位数
        $amount_to_pad = PKCS7Encoder::$block_size - ($text_length % PKCS7Encoder::$block_size);
        if ($amount_to_pad == 0) {
            $amount_to_pad = PKCS7Encoder::block_size;
        }
        //获得补位所用的字符
        $pad_chr = chr($amount_to_pad);
        $tmp = "";
        for ($index = 0; $index < $amount_to_pad; $index++) {
            $tmp .= $pad_chr;
        }
        return $text . $tmp;
    }

    /**
     * 对解密后的明文进行补位删除
     * @param decrypted 解密后的明文
     * @return 删除填充补位后的明文
     */
    public function decode($text)
    {
        $pad = ord(substr($text, -1));
        if ($pad < 1 || $pad > 32) {
            $pad = 0;
        }
        return substr($text, 0, (strlen($text) - $pad));
    }
}

/**
 * Prpcrypt class
 *
 * 提供接收和推送给公众平台消息的加解密接口.
 */
class Prpcrypt
{
    public $key;

    public function Prpcrypt($k)
    {
        $this->key = base64_decode($k . "=");
    }

    public function __construct($k)
    {
        $this->Prpcrypt($k);
    }

    /**
     * 对明文进行加密
     * @param string $text 需要加密的明文
     * @return string 加密后的密文
     */
    public function encrypt($text, $appid)
    {
        try {
            //获得16位随机字符串，填充到明文之前            
            $random = $this->getRandomStr();  
            $text = $random . pack("N", strlen($text)) . $text . $appid;
            $iv = substr($this->key, 0, 16);
            
            //使用自定义的填充方式对明文进行补位填充
            $pkc_encoder = new PKCS7Encoder;  
            $text = $pkc_encoder->encode($text);
            
            if (version_compare(PHP_VERSION, '7', '>=')) 
            {
                $encrypted = openssl_encrypt($text, 'AES-256-CBC', $this->key, OPENSSL_ZERO_PADDING, $iv);
                return array(ErrorCode::$OK, $encrypted);
            }
            else
            {
                // 网络字节序
                $size = mcrypt_get_block_size(MCRYPT_RIJNDAEL_128, MCRYPT_MODE_CBC);
                $module = mcrypt_module_open(MCRYPT_RIJNDAEL_128, '', MCRYPT_MODE_CBC, '');
                mcrypt_generic_init($module, $this->key, $iv);
                //加密
                $encrypted = mcrypt_generic($module, $text);
                mcrypt_generic_deinit($module);
                mcrypt_module_close($module);
                //print(base64_encode($encrypted));
                //使用BASE64对加密后的字符串进行编码
                return array(ErrorCode::$OK, base64_encode($encrypted));
            }
        } catch (Exception $e) {
            //print $e;
            return array(ErrorCode::$EncryptAESError, null);
        }
    }

    /**
     * 对密文进行解密
     * @param string $encrypted 需要解密的密文
     * @param string $appid appid
     * @param string $key   三方平台key
     * @return string 解密得到的明文
     */
    public function decrypt($encrypted='', $appid)
    {
        try 
        {
            if (version_compare(PHP_VERSION, '7', '>=')) 
            {
                //以下注意！！！！！
                $iv = substr($this->key, 0, 16);
                $encrypted = str_replace(' ', '+', $encrypted);
                $decrypted = openssl_decrypt($encrypted, 'AES-256-CBC', substr($this->key, 0, 32), OPENSSL_ZERO_PADDING, $iv);
            } 
            else 
            {
                //使用BASE64对需要解密的字符串进行解码
                $ciphertext_dec = base64_decode($encrypted);
                $module = mcrypt_module_open(MCRYPT_RIJNDAEL_128, '', MCRYPT_MODE_CBC, '');
                $iv = substr($this->key, 0, 16);
                mcrypt_generic_init($module, $this->key, $iv);
                //解密
                $decrypted = mdecrypt_generic($module, $ciphertext_dec);
                mcrypt_generic_deinit($module);
                mcrypt_module_close($module);
            }
        } 
        catch (Exception $e) 
        {
            return array(ErrorCode::$DecryptAESError, null);
        }
        try {
            //去除补位字符
            $pkc_encoder = new PKCS7Encoder;
            $result = $pkc_encoder->decode($decrypted);
            //去除16位随机字符串,网络字节序和AppId
            if (strlen($result) < 16) 
            {
                return "";
            }
            $content = substr($result, 16, strlen($result));
            $len_list = unpack("N", substr($content, 0, 4));
            $xml_len = $len_list[1];
            $xml_content = substr($content, 4, $xml_len);
            $from_appid = substr($content, $xml_len + 4);
            if (version_compare(PHP_VERSION, '7', '>=')) 
            {
                if (!$appid) 
                {
                    //如果传入的appid是空的，则认为是订阅号，使用数据中提取出来的appid
                    $appid = $from_appid;
                }
            }
        } 
        catch (Exception $e) 
        {
            //print $e;
            return array(ErrorCode::$IllegalBuffer, null);
        }
        if ($from_appid != $appid) 
        {
            return array(ErrorCode::$ValidateAppidError, null);
        }
        //不注释上边两行，避免传入appid是错误的情况
        if (version_compare(PHP_VERSION, '7', '>=')) 
        {
            //增加appid，为了解决后面加密回复消息的时候没有appid的订阅号会无法回复
            return array(0, $xml_content, $from_appid);
        } 
        else 
        {
            return array(0, $xml_content);
        }
    }



    /**
     * 随机生成16位字符串
     * @return string 生成的字符串
     */
    public function getRandomStr()
    {
        $str = "";
        $str_pol = "ABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789abcdefghijklmnopqrstuvwxyz";
        $max = strlen($str_pol) - 1;
        for ($i = 0; $i < 16; $i++) {
            $str .= $str_pol[mt_rand(0, $max)];
        }
        return $str;
    }
}
